1. Field of the Present Invention
The present invention relates generally to enclosures for electronic equipment, and, in particular, to thermal management in enclosures for rack-mount computer and data storage equipment.
2. Background
Racks, frames and enclosures for mounting and storing computer and other electronic components or equipment have been well known for many years. Racks and frames are typically simple rectangular frameworks on which electronic components may be mounted, or on which other mounting members, such as shelves or brackets, may be mounted which in turn may support the electronic components. Enclosures are typically frames on which panels or doors, or both, are hung to provide aesthetic improvement, to protect the components from external influences, to provide security for the components stored inside, or for other reasons.
Racks, frames and enclosures have been built in many different sizes and with many different proportions in order to best accommodate the components which they are designed to store. Components stored in these enclosures may include audio and video equipment and the like, but quite frequently include computer equipment and related peripheral devices. These components typically include housings enclosing internal operative elements.
As is also well known, the electronic equipment mounted therein tends to generate large amounts of thermal energy that needs to be exhausted away from the equipment effectively in order to maintain the equipment in proper operating order or to prevent damage thereto. The problem can be especially significant when the components are enclosed in enclosures, because thermal energy generated thereby can concentrate within the equipment enclosure and cause the components to overheat and shut down. As equipment becomes more densely packed with electronics, the quantities of thermal energy have continued to increase in recent years, and thermal energy management has become a significant issue confronting today's rack, enclosure, frame and enclosure manufacturers, the manufacturers of the electronic equipment, and the users of such equipment.
Typically, multiple racks, frames, enclosures, and the like (sometimes collectively referred to hereinafter as “enclosures”) are housed together in a data center. Because of the overheating problem, and particularly with multiple enclosures being placed in a single room or other enclosed space, thermal management of the data center is very important. A goal of data center thermal management is to maximize the performance, uptime and life expectancy of the active components being housed in the data center. This goal is generally accomplished by managing the cold air delivered to each component, and the hot air removed therefrom, such that the internal temperature of the component does not exceed the manufacturer's maximum allowable operating temperature. Preferably, the cold air delivered to the component is at or below the manufacturer's recommended temperature and in sufficient volume to meet the airflow requirements of the component, which are typically measured in cubic feet per minute (CFM).
The supply of cool air to the enclosures, and the transfer of thermal energy from the electronic equipment, is conventionally handled by the Computer Room Air Conditioner (“CRAC”). Airflow into the enclosures generally relies solely or at least primarily on the air pressure differential as measured between a raised floor plenum and the ambient room. However, active means are often used to push or pull heated air out of the enclosures.
For a particular component, thermal energy is transferred from its housing forced air convection. More specifically, internal fans may draw or push air through the housing from front-to-rear or from side-to-side over the heated internal elements within the housing. The air absorbs the thermal energy from the internal elements and carries it away as it exits the housing.
Two common problems that affect thermal management of equipment enclosures are recirculation and bypass. Recirculation occurs when hot exhaust air travels back into the component intake air stream. Recirculation can occur for a single component or for an entire enclosure. When this occurs, the exhaust airflow raises intake air temperatures and causes components to run at higher operating temperatures. Bypass occurs when cold source air bypasses the active component and travels directly into the hot exhaust air stream. Similarly to recirculation, bypass may occur for a single component or for a whole enclosure. Because cold source air is bypassing the active component, the air is not serving its intended purpose of transferring thermal energy away from the active component. As such, the bypassing air is essentially wasted, and the active component retains its thermal energy until additional cold source air contacts the active component thereby transferring the thermal energy away from the component. Based on the foregoing, it is readily apparent that bypass wastes energy. In addition, bypass contributes to humidity control problems, and can indirectly contribute to recirculation. Under ideal circumstances, all recirculation and bypass airflow can be eliminated.
Often it is difficult for side breathing, or transversely aspirated, equipment to collect inlet cooling air in a conventionally configured enclosure having a perforated or open front or back panel but having closed side panels. Typically, air enters the enclosure through perforated metal front and rear doors. As shown schematically in FIG. 1A, the airflow is routed around the enclosure frame structure, along the side space of the enclosure and around bundles of network cables (not shown) located there before turning in a generally orthogonal direction in order to enter into the equipment intake. The high velocity or momentum of the air as it makes the orthogonal turn typically generates a swirl pattern (or vortex) in the network equipment chassis. The air vortex creates the problem of recirculation that was described above. As shown in FIG. 1B, temperatures in the vicinity of a vortex zone (with temperature zones being shown by the dashed lines), and thus the temperatures of equipment located in such an area, are typically significantly higher due to the reduced heat removal associated with recirculation. More particularly, the temperature in side areas 142 is higher than the temperature in the area 140 near the intake, which is to be expected, but the air in the center of the vortex 144 is considerably higher, perhaps dangerously so, than in the other areas 140,142. Typically, imposed recirculation in fully enclosed equipment enclosures having side breathing equipment installed therein is not considered from a thermal management perspective.
Although some attention has been given to the cooling of side breathing equipment, most of this work has been focused on the containment and directing of hot exhaust air out of the enclosure. When inlet air for side breathing equipment has been addressed, the side breathing equipment has been placed in a enclosure with a vented side panel or with the side panel removed. Additionally, side breathing equipment has sometimes been installed in an open frame having no panels at all. While these solutions are valuable, it is not always possible to place side breathing equipment in a enclosure with no side panel or in an enclosure with no panels whatsoever. Accordingly, a need exists for a thermal management solution for side breathing equipment involving a more conventional enclosed enclosure.